Rotary limit switch



Sept. 6, 1960 H. MILLER ROTARY LIMIT SWITCH Filed July 15, 1957 I III I INVENTOR.

HAROLO 4-. MILLER AZTORA'IFYJ United States Patent 2,951,920 ROTARY LIMIT SWITCH Harold L. Miller, Detroit, Mich., assignor to Vemco lroducts, Inc., Detroit, Mich, a corporation of Michigan Filed July 15, 1957, Ser. No. 671,973 4 Claims. (Cl. 200-47) This invention relates to rotary limit switches and particularly to rotary limit switches that are used for controlling the operation of reversible electric motors.

Rotary limit switches are commonly used in the control of the operation of a reversible electric motor such as is found in the operating mechanisms of electrically-operated doors. The function of these switches is to limit the operation of the electric motor to a predetermined amount in each direction of rotation.

One type of such limit switch which is commonly used comprises a rotatably mounted screw shaft having a pair of switches mounted adjacent thereto and a pair of switchactuating traveling nuts threaded thereon. In addition, the switch includes a member adapted to engage notches in the periphery of the traveling nut so that when the screw shaft is rotated the traveling nuts are translated back and forth along the length of the screw shaft to operate the switches.

One disadvantage of such a rotary limit switch is that traveling nuts by using tools in order to permit the traveling nuts to be rotated to new positions on the screw shaft.

Another disadvantage of such a limit switch is that in the event that the switches, for one reason or another, do not operate to stop the operation of the motor which rotates the screw shaft, the traveling nuts will continue to be translated along the length of the screw shaft until they jam against the supports for the screw shaft, thereby causing damage to the switch. A further disadvantage of such a limit switch is that, in the event of failure of the switches, one traveling nut may jam against another to cause damage to the switch.

It is therefore an object of this invention to provide a rotary limit switch which will obviate the aforementioned disadvantages.

It is a further object of this invention to provide a rotary limit switch which can be readily adjusted without the use of tools.

It is a further object of this invention to provide a rotary limit switch which will not jam and cause damage thereto in the eventthat the switches do not function properly.

It is a further object of this invention to provide a rotary limit switch which will accurately control the operation of a controlled mechanism and will consistently provide the same results in the operation.

In the drawings:

Fig. 1 is a plan view of the limit switch embodying the invention showing the limit switch operatively connected and having the cover removed.

Fig. 2 is a sectional view taken along the line 2-2 in Fig. 1.

Fig. 3 is a fragmentary view of a portion of the limit switch shown in Fig. 2 on a greatly enlarged scale.

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cover 16 is provided and held in position by a bolt 17 and nut 18.

A shaft 19 is rotatably mounted in the casing by journals 20, 21 in end walls 14, 15, respectively. The ends of the shaft 19 project outwardly through the end walls 14, 15 and form a means whereby the screw shaft may be operatively connected either directly to the electric motor which it controls or to a mechanism operated by the electric motor. For example, a sprocket 22 may be provided on the end of the shaft and connected by an endless chain 23 to a sprocket 24 on the shaft of reversible electric motor 25.

A bracket 26 is mounted on side wall 13 by screws 27 and supports switches 28, 29 which are held on the bracket by screws 30. Switches 28, 29 are of the well-known type and include yieldingly supported switch-actuating arms 31, 32 having rollers 33, 34 on the ends thereof. Switches 28, 29 are spaced along the threaded portion 35 of the screw shaft 19 which is within the casing. Traveling nuts 36, 37 are threaded on portion 35 of shaft 19. Nut 36 is adapted to actuate switch 28 and nut 37 is adapted to actuate switch 29 as presently described.

Each nut is provided with a plurality of circumferen tially spaced and radially extending notches 38, 39, respectively, on the periphery thereof. As shown'in Figs. 1 and 2, a spring detent 40 is mounted on side wall 12 by means of nuts 41 and bolts 42 and includes a yieldable arm 43 and a lip 44 extending radially inwardly toward the center of screw shaft 19. Lip 44 extends longitudinally of the screw shaft. The lip 44 is adapted to engage one of the notches 38, 39 in the nuts 36, 37 to prevent rotation of the nuts as the screw shaft 19 is rotated,

but to permit translation of the nuts along the length of side walls 12, 13 and end walls 14, 15. A removable the screw shaft as the screw shaft 19 is rotated.

It should be understood that the switches 28, 29 are connected electrically to the control circuit for the motor 25 to stop the rotation of the motor in each direction after a predetermined operation of the motor. The control of the starting of the motor may be accomplished either through the switches 28, 29, that is, the switches may stop the rotation of the motor in one direction and initiate the rotation of the motor in the other direction; or, alternatively, the initiation of the rotation of the motor in either direction may be controlled by other means.

In operation, when the screw shaft 19 is rotated in one direction, for example, to cause translation of the nuts 36, 37 toward the left in Fig. 1, the rotation will continue until nut 36 engages roller 33 (position B) and moves arm 31 to actuate switch 28 and stop the rotation of the motor and, in turn, of the screw shaft 19. When the motor 25 operates in the other direction, rotation of the screw shaft 19 will cause the nuts 36, 37 to be'translated toward the right, as shown in Fig. 1, until traveling nut 37 contacts roller 35 and actuates switch 29.

As shown in Fig. 1, the length of lip 44 of spring detent 40 is less than the length of the threaded portion 35 of screw shaft 19. By this arrangement if, for one reason or another, the switches 28, 29 fail to operate to stop the motor and the screw shaft 19 continues to rotate, the nuts 36, 37 will be translated along the screw shaft until they move out of engagement with lip 44. Thereafter the nuts 36, 37 will rotate in unison with the screw shaft 19. For example, when the nut 36 moves to position C it will no longer rotate relative to the screw shaft, since it is out of engagement with lip 44 of spring detent 40.

The space between the ends of lip 44 and journals 20,

21 is greater than the axial dimension of both nuts 36, 37, thereby providing sufficient room for both nuts to become disengaged from lip 44 (position D in Fig. 4) and rotate in unison with screw shaft 19. It can thus be seen that by this arrangement the nuts are prevented from jamming against the journals 20, 21 in the event of failure of the switches, thereby preventing damage to the limit switch.

As shown in Figs. 1 and 4, a yieldable element 45, preferably of material such as piano wire, is provided on nut 37 and extends axially thereof toward nut 36. When the nuts 36, 37 move out of engagement with lip 44 in the event of switch failure, yieldable element 45 will engage one of the notches 38 in nut 36 before one nut jams against the other, thereby causing the nuts to move in unison and preventing any damage to the switch because of one nut jamming against the other.

In order to facilitate the return of a traveling nut to its original position after moving out of engagement with the lip 44, adjacent surfaces 47, 46 are frusto-conical or inclined. When a nut is rotated back toward the center of screw shaft 19, the inclined surfaces 47 or 46 permit arm 31, 32 of switches 28, 29 to be moved upwardly as shown in Fig. 1 without damage to the switches.

In order to adjust the operation of the limit switch, it is only necessary to remove the cover 16, manually depress the spring detent to the dotted line position shown in Figs. 2 and 3 and manually rotate the nuts 36, 37 to the newly desired position.

It can thus be seen that I have provided a rotary limit switch which can be adjusted without the use of tools and which is of a construction which will prevent damage in the event of switch or circuit failure.

I claim:

1. In a limit switch, the combination comprising a support, a screw shaft rotatab-ly mounted on said support, a pair of switches positioned adjacent said screw shaft at spaced points along the length thereof, a pair of traveling nuts threaded on said screw shaft, and a yieldable member mounted on said support and having means thereon which is yieldingly urged into engagement with the periphery of said traveling nuts to prevent rotation of said nuts as the screw shaft is rotated thereby causing said nuts to be translated along the length of said screw shaft toward and away from contact with said switches, whereby said limit switch may be readily adjusted by manually moving said yieldable member to disengage said means thereon from the periphery of the traveling nuts and manually rotating said nuts relative to said screw shaft, said yieldable member comprising a spring metal detent having "a lip which is parallel to the axis of said screw shaft and each said traveling nut being provided with a notch on its periphery which is engaged by said lip on said yieldable member, the length of said lip on said yieldable member being less than the length of the thread on said screw shaft whereby in the event said screw shaft continues to rotate after a traveling nut contacts a switch, the traveling nut will be translated along the screw shaft beyond the lip on the detent and will thereafter rotate with the screw shaft without further translation thereon, and a yieldable element on one said traveling nut and projecting toward another said traveling nut whereby when both of said traveling nuts move out of engagement with said yieldable member, said yieldable element en gages the notch in the periphery of said traveling nut and causes said traveling nuts to move in unison with the screw shaft.

2. In a limit switch, the combination comprising a support having spaced journals, a screw shaft rotatab ly mounted in said journals and having a threaded portion in the part thereof extending between said journals, a pair of switches mounted on said support adjacent said screw shaft at spaced points along the threaded portion of the screw shaft, a removable member mounted on said support adjacent said crew shaft, interengaging means between said removable member and the periphery of each said traveling nut for preventing rotation of each said traveling nut on said screw shaft when the screw shaft is rotated toward and away from contact with a switch, the length of said removable member being less than that of the threaded portion of said screw shaft whereby in the event the screw shaft continues to rotate after a traveling nut contacts a switch, the traveling nut will be translated on the screw shaft until it is out of engagement with said removable member and will thereafter rotate in unison with said screw shaft, an element on one said traveling nut, and cooperating means on the other said traveling nut adapted to be engaged by said element whereby when continuous rotation of said screw shaft causes both of said traveling nuts to be translated along the screw shaft until they are out of engagement with said removable member, the element on said one traveling nut interengages said cooperating means on the other traveling nut and causes said traveling nuts to move in unison with the screw shaft.

3. In a limit switch, the combination comprising a casing, a shaft journalled in said casing and having one end thereof projecting outwardly through the wall of the casing, said shaft having a threaded portion within said casing, a pair of switches mounted within said casing at spaced points along the length of said threaded portion of the screw shaft, a pair of traveling nuts threaded on said threaded portion of the screw shaft and adapted .to contact said switches and actuate said switches as said ing a radially extending lip adapted toengage a notch in the periphery of each said traveling nut, said yieldable member being such that said lip is yieldingly urged inwardly toward the center of each said nut, whereby the position of each said nut on said screw may be readily adjusted by manually moving said yieldable member out of engagement with the periphery of said travel ing nuts and rotating said traveling nuts relative to said screw shaft, the length of said lip on said yieldable member being less than the length of the thread on said screw shaft whereby in the event the rotation of said screw shaft is continued after a switch is contacted by a traveling nut, the traveling nut will be moved along the screw shaft past the detent and will thereafter rotate with the screw shaft Without further translation thereon, and a yieldable element on one said traveling nut and projecting toward the other said traveling nut whereby when both of said traveling nuts are translated until they are out of engagement with said yieldable member, said yieldable element engages the notch in the periphery of said other traveling nut and causes said traveling nuts to move in unison with the screw shaft.

4. In a limit switch, the combination comprising a support, a screw shaft rotatably mounted on said support, a pair of switches positioned adjacent said screw shaft at spaced points along the length thereof, a pair of traveling nuts threaded on said screw shaft, and a detent member comprising a one piece spring arm having one end thereof mounted on said support and having a lip extending along the other end thereof parallel to the axis of the screw shaft, each said traveling nut being provided with a notch on its periphery which is engaged by said lip on said spring arm thereby preventing rotation of said nut as the screw shaft is rotated and causing said nuts to be translated along the length of said screw shaft toward and away from contact with said switches, whereby said limit switch may be readily adjusted by manually moving said spring arm to disengage said means thereon from the periphery of said traveling nuts, manually rotating said nuts relative to said screw shaft, and releasing said spring arm to cause said means thereon to re-engage the periphery of said traveling nuts.

References Cited in the fileof this patent UNITED STATES PATENTS 

